Field of the Invention
The present invention relates to a positive resist composition which comprises a quinone diazide compound, an alkali-soluble resin and a specific solvent system. 2. Description of the Related Art
A composition containing a compound having a quinone diazide group (a quinone diazide compound) and an alkali-soluble resin finds use as a positive resist in the production of integrated circuits.
Recently, with integrated circuits, miniaturization has proceeded with a rise in the integration level, which results in demands for formation of patterns of sub-micron order. To form such minute patterns with good reproducibility, the positive resist composition should achieve high resolution, a large xcex3-value and a good profile and also have high qualities in various process margins such as an exposure margin and a depth of focus.
Since the width of wiring is miniaturized with the increase of the integration level, dry etching is employed in addition to wet etching. For dry etching, the resist is required to have higher resistance to dry etching, namely heat resistance than ever.
In these years, instead of a conventional mask contact printing method, a reduction projection exposure system attracts attention. One of the serious problems in this new system is low throughput. Namely, in this system, the total exposure time to expose a wafer is very long because of divided and repeated light exposure unlike a batch light exposure system which is employed in the conventional mask contact printing methods.
To solve this problem, an increase in sensitivity of the resist is most-important. If the exposure time can be shortened by an increase in the sensitivity, the throughput and in turn a yield can be improved.
One measure to increase the sensitivity is a decrease of the molecular weight of an alkali-soluble resin contained in the resist composition. However, the decrease of the molecular weight encounters some problems, for example, a large film thickness loss in an unexposed area (reduction of so-called film thickness retention), a worsening of a profile and various process margins, and a decrease of the xcex3-value because of a small difference in the dissolving rates in the developing solution between the exposed area and the unexposed area. In addition, the heat resistance of the resist is deteriorated and adhesion of the resist to a substrate is decreased disadvantageously.
Other measures to increase the sensitivity include prolongation of the developing time and increase of the concentration of an alkali in the developing liquid. However, they are not preferable since the film thickness retention and in turn the resolution are decreased.
To increase the xcex3-value, it is contemplated to increase the amount of the quinone diazide compound. But, the increase of the amount of the quinone diazide compound may lead to precipitation of fine particles of the quinone diazide compound and the alkali-soluble resin and therefore a decrease in the yield of the integrated circuits.
To solve such problems, it may be possible to use a monohydroxycarboxylate ester such as ethyl lactate which has a large dissolving capability for the quinone diazide compound and is safer with respect to human beings than the conventional resist solvent such as ethyleneglycol monoalkyl ether acetate. However, such a solvent will increase striations or cause some problem in coating such that the edge of a wafer is not coated.
An object of the present invention is to provide a positive resist composition which has a large xcex3-value and provides a good profile and a large depth of focus while maintaining other properties required for a resist such as good heat resistance, high resolution, good sensitivity and a good coating property.
According to the present invention, there is provided a positive resist composition comprising, in admixture, an alkali-soluble resin, a quinone diazide compound and a mixed solvent of (B) at least one organic solvent selected from the group consisting of xcex3-butyrolactone, 3-methoxybutanol and cyclohexanone and (A) an organic solvent other than the solvents (B) which does not have simultaneously an alkylcarbonyl group and an alkoxy group in a molecule and has a boiling point of from 140 to 180xc2x0 C. under atmospheric pressure.
In the positive resist composition of the present invention, a quinone diazide compound may be any one of conventionally used compounds. For example, a quinone diazide compound is an ester of a below described hydroxyl group-containing compound with a quinone diazide sulfonic acid such as 1,2-benzoquinone diazide-4-sulfonic acid, 1,2-naphthoquinone diazide-4-sulfonic acid or 1,2-naphthoquinone diazide-5-sulfonic acid. Preferably, a quinone diazide compound is an ester of a hydroxyl group-containing compound of the formula: 
wherein Y1xe2x80x2, Y2xe2x80x2, Z1xe2x80x2, Z2xe2x80x2, Z3xe2x80x2, Z4xe2x80x2, Z5xe2x80x2, Z6xe2x80x2 and Z7xe2x80x2 are the same and different and each a hydrogen atom, a hydroxyl group or a C1-C4 alkyl group provided that at least one of Y1xe2x80x2 and Y2xe2x80x2 is a hydroxyl group and at least two of Z1xe2x80x2, Z2xe2x80x2, Z3xe2x80x2, Z4xe2x80x2, Z5xe2x80x2, Z6xe2x80x2 and Z7xe2x80x2 are hydroxyl groups; and R1xe2x80x2, R2xe2x80x2, R3xe2x80x2, R4xe2x80x2, R5xe2x80x2 and R6xe2x80x2 are the same or different and each a hydrogen atom, a C1-C10 alkyl group, a C2-C4 alkenyl group, a C5-C8 cycloalkyl group or an aryl group, or an oxyflavan compound of the formula: 
wherein Y1 and Y2 are the same or different and each a hydrogen atom, a hydroxyl group or a C1-C4 alkyl group provided that at least one of them is a hydroxyl group; Z1, Z2, Z3, Z4, Z5, Z6 and Z7 are the same or different and each a hydrogen atom, a halogen atom, a hydroxyl group, a C1-C4 alkyl group, a C5-C8 cycloalkyl group or an aryl group provided that at least two of them are hydroxyl groups; and R1, R2, R3, R4 and R5 are the same or different and each a hydrogen atom, a C1-C10 alkyl group, a C2-C4 alkenyl group, a cyclohexyl group or an aryl group provided that at least one of R4 and R5 is a C1-C10 alkyl group, a C2-C4 alkenyl group, a cyclohexyl group or an aryl group with the above quinone diazide sulfonic acid.
Among them, the quinone diazide sulfonic acid ester of the oxyflavan (II) is preferred.
The quinone diazide compound may be prepared by a per se conventional method. For example, the quinone diazide sulfonic acid and the hydroxyl group-containing compound are condensed in the presence of a weak alkali.
Examples of the hydroxyl group-containing compound are hydroquinone, resorcinol, phloroglucin, 2,4-dihydroxybenzophenone, trihydroxybenzophenones (e.g. 2,3,4-trihydroxybenzophenone, 2,2xe2x80x2,3-trihydroxybenzophenone, 2,2xe2x80x2,4-trihydroxybenzophenone, 2,2xe2x80x2,5-trihydroxybenzophenone, 2,3,3xe2x80x2-trihydroxybenzophenone, 2,3,4xe2x80x2-trihydroxybenzophenone, 2,3xe2x80x2,4-trihydroxybenzophenone, 2,3xe2x80x2,5-trihydroxybenzophenone, 2,4,4xe2x80x2-trihydroxybenzophenone, 2,4xe2x80x2,5-trihydroxybenzophenone, 2xe2x80x2,3,4-trihydroxybenzophenone, 3,3xe2x80x2,4-trihydroxybenzophenone, 3,4,4xe2x80x2-trihydroxybenzophenone, etc.), tetrahydroxybenzophenones (e.g. 2,3,3xe2x80x2,4xe2x80x2-tetrahydroxybenzophenone, 2,3,4,4xe2x80x2-tetrahydroxybenzophenone, 2,2xe2x80x2,4,4xe2x80x2-tetrahydroxybenzophenone, 2,2xe2x80x2,3,4-tetrahydroxybenzophenone, 2,2xe2x80x2,3,4xe2x80x2-tetrahydroxybenzophenone, 2,2xe2x80x2,5,5xe2x80x2-tetrahydroxybenzophenone, 2,3xe2x80x2,4xe2x80x2,5-tetrahydroxybenzophenone, 2,3xe2x80x2,5,5xe2x80x2-tetrahydroxybenzophenone, etc.), pentahydroxybenzophenones (e.g. 2,2xe2x80x2,3,4,4xe2x80x2-pentahydroxybenzophenone, 2,2xe2x80x2,3,4,5xe2x80x2-pentahydroxybenzophenone, 2,2xe2x80x2,3,3xe2x80x2,4-pentahydroxybenzophenone, 2,3,3xe2x80x2,4,5xe2x80x2-pentahydroxybenzophenone, etc.), hexahydroxybenzophenones (e.g. 2,3,3xe2x80x2,4,4xe2x80x2,5-hexahydroxybenzophenone, 2,2xe2x80x2,3,3xe2x80x2,4,5xe2x80x2-hexahydroxybenzophenone, etc.), alkyl gallates, the compound of the formula (I), a compound which is disclosed in Japanese Patent Kokai Publication No. 269351/1990 corresponding U.S. patent application Ser. No. 07/347,065 and EP-A-0 341 608, and represented by the formula: 
wherein Y1, Y2, Y3 and Y4 are the same or different and each a hydrogen atom, a halogen atom, an alkyl group or a hydroxyl group provided that at least one of them is a hydroxyl group; Z1, Z2, Z3, Z4, Z5 and Z6 are the same or different and each a hydrogen atom, a halogen atom, an alkyl group, an aryl group or a hydroxyl group provided that at least one of them is a hydroxyl group; and X is a group of the formula: xe2x80x94C(R1)(R2)xe2x80x94 in which R1 and R2 are the same or different and each a hydrogen atom, an alkyl group, an alkenyl group, a cycloalkyl group, an alkoxyl group or an aryl group provided that when at least one of them is a hydrogen atom, an alkyl or aryl group is present at an ortho-position to a hydroxyl group which is present at an ortho-position to the group X.
As the alkali-soluble resin, polyvinylphenol, a novolak resin and the like are exemplified.
The novolak resin is prepared by a condensation reaction of a phenol with an aldehyde. Specific examples of the phenol used as one of the raw materials for the novolak resin include phenol, o-, m- or p-cresol, 2,5-, 3,5- or 3,4-xylenol, 2,3,5-trimethylphenol, 4-, 2- or 3-tert.-butylphenol, 3-, 2- or 4-ethylphenol, 3-methyl-6-tert.-butylphenol, 4-methyl-2-tert.-butylphenol, 2-naphthol, 1,3-, 1,7- or 1,5-dihydroxynaphthalene, and the like. These phenols may be used alone or in combination.
Examples of the aldehyde are aliphatic aldehydes (e.g. formaldehyde, acetaldehyde, etc.), aromatic aldehydes (e.g. benzaldehyde, o-, m- or p-hydroxybenzaldehyde, o- or p-methylbenzaldehyde, etc.) and the like.
A weight ratio of the quinone diazide compound to the alkali-soluble resin is preferably from 1:1 to 1:7.
Specific examples of the organic solvent (A) are cyclohexanol, diacetonealcohol, butylcellosolve, cyclohexanone, methyldiacetonealcohol, 2-heptanone, anisol, n-amyl acetate, n-butyl acetate, diisopropyl ketone, 2-octanone, 3-octanone and the like. They may be used independently or as a mixture of two or more of them. Among them, n-amyl acetate, 2-heptanone, anisol, 2-octanone and 3-octanone are preferred, n-amyl acetate and 2-heptanone are more preferred, and n-heptanone are most preferred.
A weight ratio of the organic solvent (A) and the organic solvent (B) is preferably from 98:2 to 30:70, more preferably from 95:5 to 40:60.
When a ratio of the organic solvent (B) is too small, the xcex3-value is decreased and the profile is worsened. When the ratio of the organic solvent (B) is too large, the coating property is deteriorated.
The solvent mixture to be used in the present invention is used in an amount that a coating film is uniformly formed on the wafer and no pin hole or no irregular coating is found. Preferably, the solvent system is used in an amount that a total amount of the quinone diazide compound and the alkali-soluble resin is from 3 to 50% by weight based on the whole weight of the resist composition.
Insofar as the effect of the present invention is not deteriorated, the resist composition of the present invention may contain another solvent such as toluene, xylene, methyl isobutyl ketone, methyl ethyl ketone, acetone, propyleneglycol monoethyl ether acetate, propyleneglycol monomethyl ether acetate, etc.
The positive resist composition is prepared by mixing and dissolving the quinone diazide compound and the alkali-soluble resin in the solvent system of the present invention.
The positive resist composition of the present invention may contain other conventionally used additives such as a sensitizer, other additional resin, a surfactant, a stabilizer or a dye which increases visibility of the formed figure and conventional additives.
The positive resist composition of the present invention has a large xcex3-value and is excellent in a profile and a depth of focus.